How can I scale something with actual measurements in meter,cm,etc?
As mentioned, Scale is unitless, it's just a multiplier for the actual Dimensions. 

The only solution is to divide the Final Dimension by the Current Dimension (FD/CD). You can type that directly into the scale value, Blender calculates it for you. So in your case type .335 / .285 which will result in a Scale of 1,17544 and your loop will have the correct dimension.